[urcu.git] / urcu-qsbr.c

/*
 * urcu-qsbr.c
 *
 * Userspace RCU QSBR library
 *
 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 *
 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
 */

#define _GNU_SOURCE
#define _LGPL_SOURCE
#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <assert.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>
#include <poll.h>

#include "urcu/wfcqueue.h"
#include "urcu/map/urcu-qsbr.h"
#define BUILD_QSBR_LIB
#include "urcu/static/urcu-qsbr.h"
#include "urcu-pointer.h"
#include "urcu/tls-compat.h"

#include "urcu-die.h"

/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
#undef _LGPL_SOURCE
#include "urcu-qsbr.h"
#define _LGPL_SOURCE

void __attribute__((destructor)) rcu_exit(void);

static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;

int32_t rcu_gp_futex;

/*
 * Global grace period counter.
 */
unsigned long rcu_gp_ctr = RCU_GP_ONLINE;

/*
 * Active attempts to check for reader Q.S. before calling futex().
 */
#define RCU_QS_ACTIVE_ATTEMPTS 100

/*
 * Written to only by each individual reader. Read by both the reader and the
 * writers.
 */
DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);

#ifdef DEBUG_YIELD
unsigned int rcu_yield_active;
DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
#endif

static CDS_LIST_HEAD(registry);

static void mutex_lock(pthread_mutex_t *mutex)
{
	int ret;

#ifndef DISTRUST_SIGNALS_EXTREME
	ret = pthread_mutex_lock(mutex);
	if (ret)
		urcu_die(ret);
#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
		if (ret != EBUSY && ret != EINTR)
			urcu_die(ret);
		poll(NULL,0,10);
	}
#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
}

static void mutex_unlock(pthread_mutex_t *mutex)
{
	int ret;

	ret = pthread_mutex_unlock(mutex);
	if (ret)
		urcu_die(ret);
}

/*
 * synchronize_rcu() waiting. Single thread.
 */
static void wait_gp(void)
{
	/* Read reader_gp before read futex */
	cmm_smp_rmb();
	if (uatomic_read(&rcu_gp_futex) == -1)
		futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1,
		      NULL, NULL, 0);
}

static void wait_for_readers(void)
{
	CDS_LIST_HEAD(qsreaders);
	int wait_loops = 0;
	struct rcu_reader *index, *tmp;

	/*
	 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
	 * indicate quiescence (offline), or for them to observe the
	 * current rcu_gp_ctr value.
	 */
	for (;;) {
		wait_loops++;
		if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
			uatomic_set(&rcu_gp_futex, -1);
			/*
			 * Write futex before write waiting (the other side
			 * reads them in the opposite order).
			 */
			cmm_smp_wmb();
			cds_list_for_each_entry(index, &registry, node) {
				_CMM_STORE_SHARED(index->waiting, 1);
			}
			/* Write futex before read reader_gp */
			cmm_smp_mb();
		}
		cds_list_for_each_entry_safe(index, tmp, &registry, node) {
			if (!rcu_gp_ongoing(&index->ctr))
				cds_list_move(&index->node, &qsreaders);
		}

		if (cds_list_empty(&registry)) {
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
				/* Read reader_gp before write futex */
				cmm_smp_mb();
				uatomic_set(&rcu_gp_futex, 0);
			}
			break;
		} else {
			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
				wait_gp();
			} else {
#ifndef HAS_INCOHERENT_CACHES
				caa_cpu_relax();
#else /* #ifndef HAS_INCOHERENT_CACHES */
				cmm_smp_mb();
#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
			}
		}
	}
	/* put back the reader list in the registry */
	cds_list_splice(&qsreaders, &registry);
}

/*
 * Using a two-subphases algorithm for architectures with smaller than 64-bit
 * long-size to ensure we do not encounter an overflow bug.
 */

#if (CAA_BITS_PER_LONG < 64)
void synchronize_rcu(void)
{
	unsigned long was_online;

	was_online = URCU_TLS(rcu_reader).ctr;

	/* All threads should read qparity before accessing data structure
	 * where new ptr points to.  In the "then" case, rcu_thread_offline
	 * includes a memory barrier.
	 *
	 * Mark the writer thread offline to make sure we don't wait for
	 * our own quiescent state. This allows using synchronize_rcu()
	 * in threads registered as readers.
	 */
	if (was_online)
		rcu_thread_offline();
	else
		cmm_smp_mb();

	mutex_lock(&rcu_gp_lock);

	if (cds_list_empty(&registry))
		goto out;

	/*
	 * Wait for readers to observe original parity or be quiescent.
	 */
	wait_for_readers();

	/*
	 * Must finish waiting for quiescent state for original parity
	 * before committing next rcu_gp_ctr update to memory. Failure
	 * to do so could result in the writer waiting forever while new
	 * readers are always accessing data (no progress).  Enforce
	 * compiler-order of load URCU_TLS(rcu_reader).ctr before store
	 * to rcu_gp_ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/* Switch parity: 0 -> 1, 1 -> 0 */
	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);

	/*
	 * Must commit rcu_gp_ctr update to memory before waiting for
	 * quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data
	 * (no progress). Enforce compiler-order of store to rcu_gp_ctr
	 * before load URCU_TLS(rcu_reader).ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/*
	 * Wait for readers to observe new parity or be quiescent.
	 */
	wait_for_readers();
out:
	mutex_unlock(&rcu_gp_lock);

	/*
	 * Finish waiting for reader threads before letting the old ptr being
	 * freed.
	 */
	if (was_online)
		rcu_thread_online();
	else
		cmm_smp_mb();
}
#else /* !(CAA_BITS_PER_LONG < 64) */
void synchronize_rcu(void)
{
	unsigned long was_online;

	was_online = URCU_TLS(rcu_reader).ctr;

	/*
	 * Mark the writer thread offline to make sure we don't wait for
	 * our own quiescent state. This allows using synchronize_rcu()
	 * in threads registered as readers.
	 */
	if (was_online)
		rcu_thread_offline();
	else
		cmm_smp_mb();

	mutex_lock(&rcu_gp_lock);
	if (cds_list_empty(&registry))
		goto out;

	/* Increment current G.P. */
	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);

	/*
	 * Must commit rcu_gp_ctr update to memory before waiting for
	 * quiescent state. Failure to do so could result in the writer
	 * waiting forever while new readers are always accessing data
	 * (no progress). Enforce compiler-order of store to rcu_gp_ctr
	 * before load URCU_TLS(rcu_reader).ctr.
	 */
	cmm_barrier();

	/*
	 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	 * model easier to understand. It does not have a big performance impact
	 * anyway, given this is the write-side.
	 */
	cmm_smp_mb();

	/*
	 * Wait for readers to observe new count of be quiescent.
	 */
	wait_for_readers();
out:
	mutex_unlock(&rcu_gp_lock);

	if (was_online)
		rcu_thread_online();
	else
		cmm_smp_mb();
}
#endif  /* !(CAA_BITS_PER_LONG < 64) */

/*
 * library wrappers to be used by non-LGPL compatible source code.
 */

void rcu_read_lock(void)
{
	_rcu_read_lock();
}

void rcu_read_unlock(void)
{
	_rcu_read_unlock();
}

void rcu_quiescent_state(void)
{
	_rcu_quiescent_state();
}

void rcu_thread_offline(void)
{
	_rcu_thread_offline();
}

void rcu_thread_online(void)
{
	_rcu_thread_online();
}

void rcu_register_thread(void)
{
	URCU_TLS(rcu_reader).tid = pthread_self();
	assert(URCU_TLS(rcu_reader).ctr == 0);

	mutex_lock(&rcu_gp_lock);
	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	mutex_unlock(&rcu_gp_lock);
	_rcu_thread_online();
}

void rcu_unregister_thread(void)
{
	/*
	 * We have to make the thread offline otherwise we end up dealocking
	 * with a waiting writer.
	 */
	_rcu_thread_offline();
	mutex_lock(&rcu_gp_lock);
	cds_list_del(&URCU_TLS(rcu_reader).node);
	mutex_unlock(&rcu_gp_lock);
}

void rcu_exit(void)
{
	/*
	 * Assertion disabled because call_rcu threads are now rcu
	 * readers, and left running at exit.
	 * assert(cds_list_empty(&registry));
	 */
}

DEFINE_RCU_FLAVOR(rcu_flavor);

#include "urcu-call-rcu-impl.h"
#include "urcu-defer-impl.h"
Commit	Line	Data
	1	/*
	2	* urcu-qsbr.c
	3	*
	4	* Userspace RCU QSBR library
	5	*
	6	* Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	7	* Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
	8	*
	9	* This library is free software; you can redistribute it and/or
	10	* modify it under the terms of the GNU Lesser General Public
	11	* License as published by the Free Software Foundation; either
	12	* version 2.1 of the License, or (at your option) any later version.
	13	*
	14	* This library is distributed in the hope that it will be useful,
	15	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	16	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	17	* Lesser General Public License for more details.
	18	*
	19	* You should have received a copy of the GNU Lesser General Public
	20	* License along with this library; if not, write to the Free Software
	21	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	22	*
	23	* IBM's contributions to this file may be relicensed under LGPLv2 or later.
	24	*/
	25
	26	#define _GNU_SOURCE
	27	#define _LGPL_SOURCE
	28	#include <stdio.h>
	29	#include <pthread.h>
	30	#include <signal.h>
	31	#include <assert.h>
	32	#include <stdlib.h>
	33	#include <stdint.h>
	34	#include <string.h>
	35	#include <errno.h>
	36	#include <poll.h>
	37
	38	#include "urcu/wfcqueue.h"
	39	#include "urcu/map/urcu-qsbr.h"
	40	#define BUILD_QSBR_LIB
	41	#include "urcu/static/urcu-qsbr.h"
	42	#include "urcu-pointer.h"
	43	#include "urcu/tls-compat.h"
	44
	45	#include "urcu-die.h"
	46
	47	/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
	48	#undef _LGPL_SOURCE
	49	#include "urcu-qsbr.h"
	50	#define _LGPL_SOURCE
	51
	52	void __attribute__((destructor)) rcu_exit(void);
	53
	54	static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
	55
	56	int32_t rcu_gp_futex;
	57
	58	/*
	59	* Global grace period counter.
	60	*/
	61	unsigned long rcu_gp_ctr = RCU_GP_ONLINE;
	62
	63	/*
	64	* Active attempts to check for reader Q.S. before calling futex().
	65	*/
	66	#define RCU_QS_ACTIVE_ATTEMPTS 100
	67
	68	/*
	69	* Written to only by each individual reader. Read by both the reader and the
	70	* writers.
	71	*/
	72	DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
	73
	74	#ifdef DEBUG_YIELD
	75	unsigned int rcu_yield_active;
	76	DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
	77	#endif
	78
	79	static CDS_LIST_HEAD(registry);
	80
	81	static void mutex_lock(pthread_mutex_t *mutex)
	82	{
	83	int ret;
	84
	85	#ifndef DISTRUST_SIGNALS_EXTREME
	86	ret = pthread_mutex_lock(mutex);
	87	if (ret)
	88	urcu_die(ret);
	89	#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
	90	while ((ret = pthread_mutex_trylock(mutex)) != 0) {
	91	if (ret != EBUSY && ret != EINTR)
	92	urcu_die(ret);
	93	poll(NULL,0,10);
	94	}
	95	#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
	96	}
	97
	98	static void mutex_unlock(pthread_mutex_t *mutex)
	99	{
	100	int ret;
	101
	102	ret = pthread_mutex_unlock(mutex);
	103	if (ret)
	104	urcu_die(ret);
	105	}
	106
	107	/*
	108	* synchronize_rcu() waiting. Single thread.
	109	*/
	110	static void wait_gp(void)
	111	{
	112	/* Read reader_gp before read futex */
	113	cmm_smp_rmb();
	114	if (uatomic_read(&rcu_gp_futex) == -1)
	115	futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1,
	116	NULL, NULL, 0);
	117	}
	118
	119	static void wait_for_readers(void)
	120	{
	121	CDS_LIST_HEAD(qsreaders);
	122	int wait_loops = 0;
	123	struct rcu_reader index, tmp;
	124
	125	/*
	126	* Wait for each thread URCU_TLS(rcu_reader).ctr to either
	127	* indicate quiescence (offline), or for them to observe the
	128	* current rcu_gp_ctr value.
	129	*/
	130	for (;;) {
	131	wait_loops++;
	132	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	133	uatomic_set(&rcu_gp_futex, -1);
	134	/*
	135	* Write futex before write waiting (the other side
	136	* reads them in the opposite order).
	137	*/
	138	cmm_smp_wmb();
	139	cds_list_for_each_entry(index, &registry, node) {
	140	_CMM_STORE_SHARED(index->waiting, 1);
	141	}
	142	/* Write futex before read reader_gp */
	143	cmm_smp_mb();
	144	}
	145	cds_list_for_each_entry_safe(index, tmp, &registry, node) {
	146	if (!rcu_gp_ongoing(&index->ctr))
	147	cds_list_move(&index->node, &qsreaders);
	148	}
	149
	150	if (cds_list_empty(&registry)) {
	151	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	152	/* Read reader_gp before write futex */
	153	cmm_smp_mb();
	154	uatomic_set(&rcu_gp_futex, 0);
	155	}
	156	break;
	157	} else {
	158	if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
	159	wait_gp();
	160	} else {
	161	#ifndef HAS_INCOHERENT_CACHES
	162	caa_cpu_relax();
	163	#else /* #ifndef HAS_INCOHERENT_CACHES */
	164	cmm_smp_mb();
	165	#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
	166	}
	167	}
	168	}
	169	/* put back the reader list in the registry */
	170	cds_list_splice(&qsreaders, &registry);
	171	}
	172
	173	/*
	174	* Using a two-subphases algorithm for architectures with smaller than 64-bit
	175	* long-size to ensure we do not encounter an overflow bug.
	176	*/
	177
	178	#if (CAA_BITS_PER_LONG < 64)
	179	void synchronize_rcu(void)
	180	{
	181	unsigned long was_online;
	182
	183	was_online = URCU_TLS(rcu_reader).ctr;
	184
	185	/* All threads should read qparity before accessing data structure
	186	* where new ptr points to. In the "then" case, rcu_thread_offline
	187	* includes a memory barrier.
	188	*
	189	* Mark the writer thread offline to make sure we don't wait for
	190	* our own quiescent state. This allows using synchronize_rcu()
	191	* in threads registered as readers.
	192	*/
	193	if (was_online)
	194	rcu_thread_offline();
	195	else
	196	cmm_smp_mb();
	197
	198	mutex_lock(&rcu_gp_lock);
	199
	200	if (cds_list_empty(&registry))
	201	goto out;
	202
	203	/*
	204	* Wait for readers to observe original parity or be quiescent.
	205	*/
	206	wait_for_readers();
	207
	208	/*
	209	* Must finish waiting for quiescent state for original parity
	210	* before committing next rcu_gp_ctr update to memory. Failure
	211	* to do so could result in the writer waiting forever while new
	212	* readers are always accessing data (no progress). Enforce
	213	* compiler-order of load URCU_TLS(rcu_reader).ctr before store
	214	* to rcu_gp_ctr.
	215	*/
	216	cmm_barrier();
	217
	218	/*
	219	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	220	* model easier to understand. It does not have a big performance impact
	221	* anyway, given this is the write-side.
	222	*/
	223	cmm_smp_mb();
	224
	225	/* Switch parity: 0 -> 1, 1 -> 0 */
	226	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR);
	227
	228	/*
	229	* Must commit rcu_gp_ctr update to memory before waiting for
	230	* quiescent state. Failure to do so could result in the writer
	231	* waiting forever while new readers are always accessing data
	232	* (no progress). Enforce compiler-order of store to rcu_gp_ctr
	233	* before load URCU_TLS(rcu_reader).ctr.
	234	*/
	235	cmm_barrier();
	236
	237	/*
	238	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	239	* model easier to understand. It does not have a big performance impact
	240	* anyway, given this is the write-side.
	241	*/
	242	cmm_smp_mb();
	243
	244	/*
	245	* Wait for readers to observe new parity or be quiescent.
	246	*/
	247	wait_for_readers();
	248	out:
	249	mutex_unlock(&rcu_gp_lock);
	250
	251	/*
	252	* Finish waiting for reader threads before letting the old ptr being
	253	* freed.
	254	*/
	255	if (was_online)
	256	rcu_thread_online();
	257	else
	258	cmm_smp_mb();
	259	}
	260	#else /* !(CAA_BITS_PER_LONG < 64) */
	261	void synchronize_rcu(void)
	262	{
	263	unsigned long was_online;
	264
	265	was_online = URCU_TLS(rcu_reader).ctr;
	266
	267	/*
	268	* Mark the writer thread offline to make sure we don't wait for
	269	* our own quiescent state. This allows using synchronize_rcu()
	270	* in threads registered as readers.
	271	*/
	272	if (was_online)
	273	rcu_thread_offline();
	274	else
	275	cmm_smp_mb();
	276
	277	mutex_lock(&rcu_gp_lock);
	278	if (cds_list_empty(&registry))
	279	goto out;
	280
	281	/* Increment current G.P. */
	282	CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR);
	283
	284	/*
	285	* Must commit rcu_gp_ctr update to memory before waiting for
	286	* quiescent state. Failure to do so could result in the writer
	287	* waiting forever while new readers are always accessing data
	288	* (no progress). Enforce compiler-order of store to rcu_gp_ctr
	289	* before load URCU_TLS(rcu_reader).ctr.
	290	*/
	291	cmm_barrier();
	292
	293	/*
	294	* Adding a cmm_smp_mb() which is _not_ formally required, but makes the
	295	* model easier to understand. It does not have a big performance impact
	296	* anyway, given this is the write-side.
	297	*/
	298	cmm_smp_mb();
	299
	300	/*
	301	* Wait for readers to observe new count of be quiescent.
	302	*/
	303	wait_for_readers();
	304	out:
	305	mutex_unlock(&rcu_gp_lock);
	306
	307	if (was_online)
	308	rcu_thread_online();
	309	else
	310	cmm_smp_mb();
	311	}
	312	#endif /* !(CAA_BITS_PER_LONG < 64) */
	313
	314	/*
	315	* library wrappers to be used by non-LGPL compatible source code.
	316	*/
	317
	318	void rcu_read_lock(void)
	319	{
	320	_rcu_read_lock();
	321	}
	322
	323	void rcu_read_unlock(void)
	324	{
	325	_rcu_read_unlock();
	326	}
	327
	328	void rcu_quiescent_state(void)
	329	{
	330	_rcu_quiescent_state();
	331	}
	332
	333	void rcu_thread_offline(void)
	334	{
	335	_rcu_thread_offline();
	336	}
	337
	338	void rcu_thread_online(void)
	339	{
	340	_rcu_thread_online();
	341	}
	342
	343	void rcu_register_thread(void)
	344	{
	345	URCU_TLS(rcu_reader).tid = pthread_self();
	346	assert(URCU_TLS(rcu_reader).ctr == 0);
	347
	348	mutex_lock(&rcu_gp_lock);
	349	cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
	350	mutex_unlock(&rcu_gp_lock);
	351	_rcu_thread_online();
	352	}
	353
	354	void rcu_unregister_thread(void)
	355	{
	356	/*
	357	* We have to make the thread offline otherwise we end up dealocking
	358	* with a waiting writer.
	359	*/
	360	_rcu_thread_offline();
	361	mutex_lock(&rcu_gp_lock);
	362	cds_list_del(&URCU_TLS(rcu_reader).node);
	363	mutex_unlock(&rcu_gp_lock);
	364	}
	365
	366	void rcu_exit(void)
	367	{
	368	/*
	369	* Assertion disabled because call_rcu threads are now rcu
	370	* readers, and left running at exit.
	371	* assert(cds_list_empty(&registry));
	372	*/
	373	}
	374
	375	DEFINE_RCU_FLAVOR(rcu_flavor);
	376
	377	#include "urcu-call-rcu-impl.h"
	378	#include "urcu-defer-impl.h"